The present invention relates to an improvement in the area of polyurethane dispersion resins and an improvement in the penetrating stains/sealants art. The improvement comprises the addition of an active-hydrogen containing composition having only one active-hydrogen and also having a long aliphatic chain, such as an alcohol or a monoamine than contains a C6 or greater aliphatic chain, as part of the prepolymer reaction mixture. This composition reacts with the isocyanate groups during the formation of the prepolymer. As a result, the prepolymer has both isocyanate functionality and contains a hydrophobic end group. The prepolymer is neutralized, dispersed in water and chain extended to a composition that penetrates into porous substrates and exhibits excellent water repellency due to the inclusion of the hydrophobic aliphatic end group. Introducing long hydrophobic end groups imparts excellent water resistance and beading characteristics, even to a low molecular weight dispersion polymer. Such low molecular weight polymers would otherwise be expected to show early water sensitivity.
Finishes which are useful on porous substrates such as wood, concrete, cement, brick and the like typically fall into two broad classifications: surface coatings and penetrating finishes. Surface coatings can be very high molecular weight, can be highly crosslinked, and characteristically form a continuous film over the substrate. Varnishes and polyurethane clearcoats are typically classified as surface coatings.
Penetrating finishes, on the other hand, are designed to protect a substrate, and typically change a substrate's color, yet retain the natural textural appearance of the substrate. Penetrating pigmented stains, non-pigmented wood preservatives, and water sealants are typical examples of penetrating finshes. One key attribute of penetrating finishes is that they are designed so as not to form an appreciable surface film or coating on the wood/substrate. They are typically low in molecular weight and very small particle size. They are durable, well suited for textured, exposed surfaces such as siding, decks, steps and the like, can contain water repellants, and are easily applied. The ability to penetrate into the surface without leaving a significant or appreciable film on the surface virtually eliminates the peeling and cracking that varnishes and surface coatings experience.
Penetrating finishes can be further subdivided as clear systems or colored systems. The clear systems typically contain a water repellant. When applied to a wood or porous substrate, these compositions serve to protect the substrate from moisture. In addition to their protective characteristics, the colored systems are designed to change the color of the wood or porous surface without hiding the grain or texture of the substrate.
This invention is directed to penetrating finishes, particularly, penetrating stains and water sealants. In the past, commercial architectural penetrating stains and water sealants have been formulated from oil-based compositions. Many commercially available wood stains still utilize pure linseed oil. Oil-based compositions are relatively inexpensive and provide good spreading characteristics. However, such stains typically lack good abrasion resistance and good drying characteristics. They are, furthermore, typically very high in volatile organic compounds content (VOC).
With the advent of environmental laws and regulations controlling the maximum amounts of VOC permitted in paints, coatings, stains, sealants and the like, numerous attempts have been made in the prior art to formulate penetrating stains which comply with the VOC requirements.
For example, European Patent Application 0 314 378 A1 to Adkins discloses a waterbome alkyd deck stain containing a medium-long oil length water-reducible alkyd resin solubilized in water with the use of propylene glycol tertiary butyl ether as a coupling solvent. Adkins claims to have low VOC, good resistance to water, durability to abrasion and the like.
Likewise, U.S. Pat. No. 4,276,329 to Vasishth et al. discloses a composition for treating and protecting wood surfaces comprising a low molecular weight alkyd resin in a cosolvent of water and glycol ether.
U.S. Pat. No. 4,432,797 to Vasishth et al. discloses a water based thickened stain containing a film forming resin, pigment, thickener and water. The resin is taught to be either an alkyd, a water based acrylic or a water solution of a modified polysaccharide polymer.
UK Patent Application 2 215 732 A to Timperley discloses a water based wood staining composition comprising a water soluble acrylic resin and a pigment.
UK Patent 1 589 605 to Gorivaerk disclose a method of preparing a penetrating wood stain of a suspension of finely divided solids in an oil-in-water emulsion.
U.S. Pat. No. 5,310,780 relates to previous work of one of the present inventors. The present invention represents a substantial improvement over the '780 patent. The improvement comprises the addition of an active-hydrogen containing composition, containing only one active hydrogen and also containing a long aliphatic chain, such as an alcohol or a monoamine containing a C6 or greater aliphatic chain, as part of the prepolymer reaction mixture.
U.S. Pat. No. 5,354,807 to Dochniak discloses anionic water dispersed polyurethane polymers that comprise the reaction product of a polyisocyanate, an active-hydrogen containing compound such as a polyol and a diamine monomer containing a pendant aliphatic.